The present invention relates to a method of sharing duplex channels in an automatic channel selection system; and more specifically, to a method of sharing a predetermined number of duplex channels in a frequency band of an automatic selection system. The stations comprising this system continuously scan all the receiving channels in the duplex band assigned to them, in the resting condition, each searching for its own address code. The signalling phase for setting up a connection between a first (calling) station and a second (called) station includes the following steps: the calling station stops the aforesaid scanning process and searches for a free receiving channel; after such a channel has been found, the transmitter of the calling station starts transmitting at the frequency of the relevant duplex channel over which, subsequently, the address code of the called station is transmitted; as soon as the called station recognizes its own address code, this station will stop the aforesaid scanning process carried out thus far, after which its transmitter will start transmitting on the relevant duplex channel a vertification signal to the calling station; after verification by the calling station the connection will be established and information can be exchanged.
The invention further relates to an automatic channel selection system for sharing a predetermined number of duplex channels in a frequency band in which the aforesaid method is realised. The channel selection system comprises a plurality of stations, each of which is provided with a duplex transmit/receive arrangement; scanning circuits for scanning all the receiving channels in the duplex band assigned to that station, searching for the address code assigned to the relevant station; a first switching circuit for rendering the scanning circuits inoperative when a connection to another station is to be initiated or if the address code assigned to the relevant station is recognised; and a second switching circuit to activate the transmitter when a free receiving channel has been found for a possible connection to be set up to another station or if a verification signal is to be transmitted after the address code assigned to the relevant station has been recognized.
Such a method and such an automatic channel selection system can be utilized for wireless telephone sets and mobile radio services without central control.
When applying the aforesaid method, problems may arise: if there is a connection between a first and a second station of the system over duplex channels at certain frequencies and a connection is to be set up between a third and a fourth station of the system over duplex channels at these frequencies, while the calling station of the latter pair is unable for whatever reason to receive signals transmitted by the calling station of the former stations whose transmission frequency corresponds to the frequency which the receiving channel of the calling station is tuned to, this called station will receive signals from both the calling station and either one of the former stations provided that the called station of the latter pair is not only within the range of the calling station but also within the range of either one of the former stations. If the signals of the calling station are received stronger than those from either of the former stations, a connection is realised between the third and fourth stations, which connection may become useless by mutilation and may disturb the conversation in progress over the connection between the first and second stations such that this connection has to be broken off.